Celestials were once all members of the angelic host... a strict but kind hierarchy of angels who each knew and understood their place. The host was broken up into seven choirs, each with a single angel at it's head... with Aevum himself as the ultimate ruler of them all. Now, the choirs are broken, and the host is scattered throughout the world, most angels acting as independent forces.
Physically, celestials are magestic and beautiful creatures. They appear as tall humanoids bathed in holy light, with large bird-like wings that sweep out from their backs. They are beautiful almost without fail, and their very appearance brings awe in lesser beings. Their emotions radiate from them, and are almost impossible to hide. Usually, such emotions are peaceful and benevolent, inspiring hope and comfort in those around them. An angel's wrath is terrifying to behold, and few mortals can bring themselves to stand against it. Likewise, an angel in misery or mourning is like a mire of despair that pulls in everyone around it, and can lead as far as complete detachment or suicide. As such, angels can be some of the most inspiring and uplifting, or unintentionally destructive beings upon creation.